Apparatus of this type are well known and attempts are being made at all times to improve the operation and portability of these devices so that they can be carried by many persons travelling in remote locations where their safety may be compromised.
One area of continual difficulty is that of the battery power supply so that efforts to reduce power usage remain a high priority.
One way to reduce power usage is to require the user to turn off the system when not required for example when the user is stationary in camp. However the user cannot always be relied upon to remember such details particularly where the environment is stressful.